1. Field of Applicable Technology
The present invention relates to an apparatus for audio reproduction utilizing audio signals produced from an audio signal source such as a compact disc player, and in particular to an apparatus for controlling such an audio reproduction apparatus by supplying respective digital codes, to produce various arbitrary sound fields which will reproduce desired acoustic characteristics such as those of a concert hall etc.
2. Prior Art Technology
In recent years, various new types of audio and audio-visual apparatus have been developed, such as compact disc players, digital audio tape recorders, high-fidelity video recorders, high-definition television systems, etc. Accompanying these developments, the need has arisen for equipment which will enable various arbitrary sound fields to be produced, utilizing the audio signals that are produced from such a new type of audio or audio-visual apparatus For example it may be desired to produce within a small listening room a sound field which will give the impression to a listener of being within a large concert hall. Alternatively, it may be desired to vary the sound field such as to suitably match a video display with an audio output which is being concurrently generated e.g. to control the sound field that is produced by loudspeakers which are reproducing audio signals derived from the sound track of a video recorder, such that the acoustic impression that is conveyed to a listener/viewer will be matched to the video images that are being concurrently produced. Various methods of altering such a sound field may be envisaged. Such alteration could consist for example of simply varying the sound volume emitted from one or more loudspeakers in accordance with the apparent distance of a sound-emitting object or person that appears in a corresponding video image, or varying the position (within a specific listening region) at which such a sound-emitted object or person seems (to a user situated within that region) to be located in the listening region. The latter type of apparent position variation could be executed in two dimensions within the listening region, by using at least two loudspeakers, or in three dimensions, by using a more complex arrangement of loudspeakers. However it should be noted that the scope of the present invention also applies to an apparatus whereby sound field alteration is performed very simply, by controlling an audio signal such as to vary the sound volume that is produced from one or more loudspeakers.
It is now possible to readily process audio signals by digital circuits such as to convert the audio signals to a form which will reproduce a desired sound field within a specific listening region, e.g. when the converted audio signals are supplied to respective channels of a multi-channel audio amplifier and loudspeaker system. In the case of digital audio signals obtained from a source such as a compact disc player, such digital processing can be directly executed. If the audio signals are originally of analog form, they can be converted to digital form by digital/analog conversion and then digitally processed.
In the prior art, systems have been proposed for controlling an audio signal produced by an audio-visual apparatus, to reproduce various arbitrary sound fields. Such a prior art system basically consists of an apparatus for producing an input audio signal (e.g. the audio signal playback section of a video cassette recorder, abbreviated in the following to VCR), a sound field variation circuit for processing that input audio signal to obtain audio signals that will reproduce specific sound fields, with the particular sound field that is reproduced being determined by a digital control code that is supplied to the sound field variation circuit, stereophonic (or quadraphonic) amplifiers and loudspeakers driven by the output audio signals from the sound field variation circuit to thereby generate the desired sound fields within a listening region, and a section for generating respective digital control codes which are inputted to the sound field variation circuit to obtain desired corresponding sound fields. Assuming that such a system is used with a VCR, the operation is as follows. As a listener/viewer observes a video display that is generated from a video signal produced from the VCR, he can selectively vary the sound field with which the audio signals from the VCR are reproduced, by actuating the control code generating section to input corresponding control codes to the sound field variation circuit. In this way, whereas the actual contents of the audio signals that are reproduced within the listening region are determined by the audio signals produced by playback from the VCR, the characteristics of the sound field that is thereby produced within the listening region are selectively determined by the listener, by inputting specific control codes.
In this way, the listener can vary the sound field within the listening region such as to appropriately match the images that are currently being produced from the VCR video signal, by manually selecting successive control codes that are supplied to the sound field variation circuit. However each time the listener/viewer plays that audio/visual material using the VCR, it is necessary to repeat this sequence of manual operations for selecting the control codes such as to match the video images.